As known, a lens module that is driven by a voice coil motor (VCM) is advantageous for reducing the overall size of the lens module and lowering the product price. Nowadays, the voice coil motor is applied to the lens module having an auto focus function and/or an auto macro function. The auto focus function enables the optical system to obtain correct focus on a subject without requiring the operator to manually adjust focus. The auto macro function allows for close-up shots when the distant from the subject is very short.
FIG. 1 is a schematic exploded view illustrating a lens module that is driven by a voice coil motor according to the prior art. The lens module 10 principally comprises an upper coupling element 11, an upper spring 12, a magnet yoke 13, several magnets 14, a coil 15, a lens holder 16, a cushion 17, a lower spring set 18 including two springs 181 and 182, and a lower coupling element 19.
FIG. 2A is a schematic rear view illustrating the magnet yoke of the lens module shown in FIG. 1. FIG. 2B is a schematic side view of the magnet yoke shown in FIG. 2A taken from the line AA′. FIG. 2C is a schematic partially enlarged view of the magnets shown in FIG. 1. FIG. 3A is a schematic rear view illustrating the lens holder of the lens module shown in FIG. 1. FIG. 3B is a schematic side view of the lens holder shown in FIG. 3A taken from the line BB′. FIG. 4A is a schematic top view illustrating the lower coupling element of the lens module shown in FIG. 1. FIG. 4B is a schematic side view illustrating the retaining post of the lower coupling element shown in FIG. 4A taken from the line CC′.
Hereinafter, the configurations and the operations of the conventional lens module 10 will be illustrated in more details with reference to FIGS. 1, 2, 3 and 4.
As shown in the drawings, several engaging posts 111 are extended downwardly from the edges of the upper coupling element 11 along the axial direction 101. The upper spring 12 is disposed under the upper coupling element 11. An elastic serpentine structure 123 is arranged between a lower inner rim 121 and an upper outer rim 122 of the spring 12. The lower inner rim 121 and the upper outer rim 122 are disposed on different planes in the spatial space.
The magnet yoke 13 is disposed under the upper spring 12. The magnet yoke 13 has an inner wall 131 and an outer wall 132. The inner wall 131 is cylindrical and concentric with the outer wall 132. The magnet yoke 13 is annular and open toward the bottom. The upper end of the magnet yoke 13 is closed by a top wall 133 between the cylindrical inner wall 131 and the outer wall 132. That is, the outer wall 132 is extended downwardly from the periphery of the top wall 133 and encloses the cylindrical inner wall 131. In addition, the axial height of the cylindrical inner wall 131 is smaller than the axial height of the outer wall 132. In other words, the cylindrical inner wall 131, the bottom 1331 of the top wall 133 and the outer wall 132 collectively define an open concave space (as shown in FIGS. 2A and 2B). Moreover, the magnets 14 are attached on the inner surface 1321 of the outer wall 132 of the magnet yoke 13.
The lens holder 16 is tubular and has a thread structure 161 formed on the inner surface thereof, so that a lens (not shown) is fixed onto the thread structure 161. In addition, an annular flange 1621 is circumferentially and outwardly extended from the lower periphery 162 of the lens holder 16 so as to support the coil 15 thereon. The annular flange 1621 has several retaining holes 16211 that are circumferentially arranged at regular intervals. During the lens module 10 is operated, the annular flange 1621 is sustained against the bottom 1311 of the cylindrical inner wall 131 of the magnet yoke 13.
The lower coupling element 19 has several engaging grooves 191 and several retaining posts 193. The engaging grooves 191 mate with the engaging posts 111 of the upper coupling element 11. The retaining posts 193 are disposed on the lower surface 192 of the lower coupling element 19 and mate with the retaining holes 16211 of the lens holder 16. Via the engagement between the engaging grooves 191 and the engaging posts 111 and the engagement between the retaining posts 193 and the retaining holes 16211, the upper coupling element 11, the upper spring 12, the magnet yoke 13 with the attached magnets 14, the lens holder 16 with the supported coil 15, the cushion 17, the lower spring set 18 and the lower coupling element 19 are combined together to assemble the lens module 10.
The position of the lens holder 16 is controlled by applying current through the coil 15. Since the magnets 14 provide a permanent magnetic field, any current passing through the coil 15 will cause a magnetic force to be generated on the coil 15 while moving the lens holder 16 toward the springs. The principles of implementing the auto focus function or the auto macro function by the voice coil motor are known in the art, and are not redundantly described herein.
The lens module having the auto focus function or the auto macro function according to the conventional techniques, however, still has some drawbacks. For example, as shown in FIG. 2B, the magnets 14 have respective arcuate surfaces 141 mating with the four chamfered corners 1322 of the outer wall 132 of the magnet yoke 13 such that the magnets 14 can be attached on the cylindrical inner walls 1321 of the chamfered corners 1322. Since the curvature of the chamfered corner 1322 is difficult to be precisely controlled in the fabricating process, the curvature of the arcuate surface 141 is possibly inconsistent with the curvature of the chamfered corner 1322. Under this circumstance, the magnet 14 fails to be securely attached onto the cylindrical inner wall 1321 of the chamfered corner 1322 and readily falls down. Moreover, since the size of the lens module 10 is very small, the retaining posts 193 are possibly broken during the retaining holes 16211 of the lens holder 16 are coupled with the retaining posts 193. Under this circumstance, the yield of the lens module 10 is decreased. For achieving the coupling efficacy, the retaining hole 16211 should have a sufficient depth. In other words, since the thickness of the annular flange 1621 of the lens holder 16 fails to be considerably reduced, it is detrimental to reduction of the overall size of the lens module.
Therefore, there is a need of providing a lens module that is driven by a voice coil motor so as to obviate the drawbacks encountered from the prior art.